This invention relates to optical fiber communicating networks and links. More specifically, this invention provides an apparatus to couple multiple fiber inputs and outputs to provide selective optical tapping or wavelength division multiplexing.
Optical fiber communications systems have been firmly established as a cost competitive alternative to other types of communications methods for numerous applications in telecommunications, computer networks, and many other areas. To take full advantage of optical transmission requires using the unique properties of optical fibers coupled to various devices particularly to light sources such as semiconductor lasers and light emitting diodes and to optical detectors such as PIN photodiodes and avalanche photodiodes (APD's).
A single optical fiber can be made to carry two or more separate optical signals operating at different wavelengths using independent light sources and detectors at the end devices or terminals. Each optical wavelength pathway can then be multiplexed by other methods such as frequency, space or time division multiplexing, to provide a link or network with a very high bandwidth capacity. All such links or networks using multiplexing of two or more wavelengths require special devices to mix and split the various optical pathways.
The general term wavelength division multiplexing devices applies to those optical components capable of coupling into or splitting out of an optical waveguide or fiber, two or more wavelengths of optical information. The general term is often abbreviated as WDM. Devices which can both couple and split two or more wavelengths into or from an optical beam are called wavelength division multiplexers, mixers and splitters or simply WDM mixer-splitters.
Prior to the subject invention WDM mixer-splitters have been made by various techniques usually requiring graded index lenses, and/or elaborate alignment procedures and equipment, in order to achieve low insertion losses. Additionally at least some prior WDM devices and optical taps used coatings such as partially reflective or dichroic filter coatings external to the optical fiber such as on a thin glass plate or on a beamsplitter prism or cube.
Although such prior systems have achieved a degree of operability and acceptance, such acceptance has not been without reservation. In this connection prior systems have proven to be somewhat large, complicated and expensive. Moreover, prior coating techniques tend to increase cross-talk between channels and further tend to increase insertion loss of the device by adding reflective surfaces.
The difficulties suggested in the preceding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness and user satisfaction of prior WDM mixer-splitter devices. Other noteworthy problems may also exist, however those outlined above should be sufficient to demonstrate that WDM mixer-splitters appearing in the past will admit to worthwhile improvement.
OBJECTS OF THE INVENTION p It is therefore a general object of the invention to provide a novel WDM mixer-splitter which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a WDM mixer-splitter having low insertion losses.
It is another object of the invention to provide a WDM mixer-splitter with reduced cross-talk between channels.
It is yet another object of the invention to provide a WDM mixer-splitter with reduced reflection losses.
It is a further object of the invention to provide a WDM mixer-splitter which may be facilely and economically manufactured.
It is yet a further object of the invention to provide a WDM mixer-splitter which may be facilely mass produced for multiple wavelength tapping or multiplexing.